The present invention relates to a method for supplying power to a copying machine, and more particularly for applying a symmetric AC voltage to a photosensitive drum to generate an asymmetric AC potential on the surface of the drum so that a picture image of good quality can be obtained and stability of the surroundings can be improved.
Furthermore, in the present invention, the symmetric AC power and DC power instead of the conventional asymmetric AC power, where the configuration of circuit is complicated, are used for high voltage circuit so that the configuration of power circuit can be further simplified.
As shown in FIG. 1, the prior conventional copying machine comprises a photosensitive drum (1) which consists of a photosensitive body (1a) formed on the surface thereof and a supporting member (1b) for supporting the photosensitive body (1a), the an electrifier (2) for generating a uniform surface potential on the surface of the photosensitive drum (1) and electrifier power supply portion (3) for supplying a predetermined power to the electrifier (2), the enveloper (not shown) for enveloping the predetermined portion of the surface of the photosensitive drum (1) corresponding to the picture image to change the surface potential, a developer (4) consisting of a toner to be attached to the enveloped (or illuminated) portion or the unenveloped (or non-illuminated) portion of the surface of the photosensitive drum (1), a developer roller (5) for attaching toner to the enveloped portion or the unenveloped portion, the developer power supply portion (6) for supplying the predetermined power to the developer and the developer roller (5), a transcriber (7) for transferring and attaching toner attached to the predetermined portion of the surface of the photosensitive drum (1) to the paper, a transcriber power supply portion (8) for supplying the predetermined power to the transcriber (7), a discharging brush (9), to which the predetermined power is applied for discharging the charge generated on the surface of the transcribed paper through the transcriber (7), a discharging brush power supply portion (15) for supplying a predetermined power to the discharging brush (9), the cleaning blade (10) for scratching toner which is not transcribed to the paper but is remained on the surface of the photosensitive drum (1), a cleaning portion (11) for storing toner scratched by the cleaning blade (10), a front guide (12) for guiding the transcribing paper between the photosensitive drum (1) and the transcriber (7), a rear guide (13) for guiding the paper in which the toner is transcribed to be outputted and a guide power supply portion (14) for supplying a predetermined power to the front guide (12).
The above constituent elements will be described in detail as follows.
First, the photosensitive drum (1) consists of the photosensitive body (1a) formed on the surface thereof and the conductive supporting member (1b) for supporting said photosensitive body (1a) and said conductive supporting member (1b) is electrically grounded (0 V).
Furthermore, in general corona electrifier has been used for the electrifier (2) but in the copying machine as shown in FIG. 1, a roller electrifying method is used, which is now mostly used. The asymmetric AC power is used for the electrifier power supply portion (3) to increase the electrifying capability. The developer (4) consists of the developer roller (5) for smearing toner stored within with uniform depth and transferring it to the photosensitive drum (1) and the peripheral apparatus. The asymmetric AC power is used for the developer power supply portion (6) also to increase visibility of the developing picture image.
On the other hand, in general, corona transcriber has been used for the transcriber (7) but in the copying machine as shown in FIG. 1, a roller transcribing method is used, which is now mostly used. The symmetric AC power of a predetermined level is used for the transcriber power supply portion (8). The front guide (12) and the rear guide (13) are established in the peripheral of the transcriber (7). The symmetric AC power is used for the guide power supply portion (14) as well. In addition, the cleaning portion (11) and the cleaning blade (10) are equipped.
The operation of the conventional copying machine will be described as follows.
First, if the photosensitive drum (1) is rotated, the charge is accumulated on the surface of the photosensitive drum (1) by the electrifier (2) and the uniform surface potential is generated. If the photosensitive drum (1) reaches an enveloping position and light is radiated, the charge accumulated on the surface of the photosensitive drum (1) is discharged to the conductive supporting member (1b) in accordance with the quantity of the radiated light and the surface potential of the photosensitive drum (1) is changed.
Accordingly, the photosensitive drum (1) of which the surface charge is different in accordance with each portion, reaches the developer (4) by light radiated through the enveloper where toner is attached with a predetermined depth by the developer roller (5) and an electric field is applied from the developer power supply portion (6). Toner of fixed quantity is attached on the surface of the photosensitive drum (1) in accordance with the surface potential of the photosensitive drum (1).
Henceforth, if the photosensitive drum (1), where toner is attached, is adhered closely to the paper transferred by the front guide (12) and then reach the transcriber (7), toner attached on the surface of the photosensitive drum (1) is transferred to the paper by the magnetic field applied by the transcriber power supply portion (8). On the other hand, toner which is not transcribed is scratched from the photosensitive drum (1) by the cleaning blade (10) and it is stored in the cleaning portion (11) as disused toner.
FIG. 2 shows changes of the surface potential generated in each position of the peripheral of the photosensitive drum (1) and movement of toner as a graph.
As mentioned above, a method for supplying power to a copying machine of the prior art could be improved in the performance of a electrifier and a developer by applying the asymmetric AC power thereto. But, from a practical point of view, because configuration of circuit for generating the high asymmetric current is more complicated than that of a high DC voltage circuit or a symmetric AC power circuit, the unit cost of the product rises. Furthermore, because the asymmetric AC power, as shown in FIG. 3(A), is applied to the surface of the photosensitive drum (1) during enveloping and the symmetric AC power, as shown in FIG. 3(B), is applied during unenveloping, toner smeared on the surface of the photosensitive drum is not thinly attached over the whole surface and may be projected upward so that the quality of the picture image is degraded.